The present invention relates to a linear predictive speech analysis-synthesis apparatus and, more particularly, to an improvement of a synthesis side thereof.
In a conventional linear predictive speech analysis-synthesis apparatus, an impulse train having repetition frequency of a fundamental frequency of an input speech signal is used generally as an exciting source signal on the synthesis side in case the input speech signal is of a voice sound. An example of this type is disclosed in U.S. Pat. No. 4,301,329 bearing the title of "SPEECH ANALYSIS AND SYNTHESIS APPARATUS", assigned to this applicant.
In another conventional speech analysis-synthesis apparatus, a pulse train having a shape corresponding to an envelope waveform which is repeated at a fundamental frequency is also used instead of the impulse train.
The above-mentioned conventional linear predictive speech analysis-synthesis apparatuses have the following shortcoming. In the former apparatus which utilizes the impulse train as the exciting source signal, energy concentrates on a pitch excitation point on the time axis and, thus, a synthesized output speech signal becomes unnatural. In the latter which utilizes a shaped pulse train, the exciting source signal becomes colored while the concentration of energy is avoided. Thus, a synthesized output speech signal becomes different from an input speech signal in a spectral structure, which results in unnaturalness.